1. Field of the Invention
The present invention relates to a wrench, especially to a unidirectional ratchet wrench.
2. Description of the Prior Arts
With reference to FIG. 7, a conventional unidirectional ratchet wrench is used to drive a bolt and comprises a handle, a head 40 and a ratchet assembly.
The head 40 is formed on the handle and has two edges, a stationary jaw 42, a ratchet jaw 43 and a cavity 41.
The stationary jaw 42 is formed on and protrudes from one edge of the head 40 and has an inner surface.
The ratchet jaw 43 is formed on and protrudes from the other edge of the head 40 and has an inner surface, a slot 431, two recesses 432 and two sides. The slot 431 is defined in the inner surface of the ratchet jaw 43 and has an inner end. The recesses 432 are defined in the sides of the ratchet jaw 43 and communicate with the slot 431.
The cavity 41 is formed between the jaws 42, 43 and has a peripheral surface and multiple recesses. The multiple recesses are formed in the peripheral surface of the cavity 41 at intervals to provide a ratcheting space when the head 40 is rotated around a bolt head in a non-drive direction.
The ratcheting assembly is mounted in the ratchet jaw 43 and has a tapered coil spring 44, a retractable tab 45 and two cover plates 46.
The tapered coil spring 44 is mounted in the slot 431 and has an outer end.
The retractable tab 45 is moveably mounted in the slot 431 and has an abutting surface. The retractable tab 45 abuts the outer end of the tapered coil spring 44. The abutting surface of the retractable tab 45 projects into the cavity 41.
The two cover plates 46 are respectively mounted in the recesses 432 in the ratchet jaw 43.
The bolt head has multiple flats and multiple corners formed between adjacent flats. When using the conventional unidirectional ratchet wrench, the peripheral surface of the cavity 41 and the abutting surface of the retractable tab 45 engage the flats of the bolt head. In order to tighten the blot, a torque is applied to the blot head by a turning stroke in the drive direction. When the conventional unidirectional ratchet wrench is rotated in the non-drive direction the retractable tab 45 is pressed into the slot 43 by the corners of the bolt head to disengage the tab 45 from the blot head. Thus, the head 40 can be rotated in the non-drive direction to allow the conventional unidirectional ratchet wrench to be rotated within a limited arc without realigning the head 40 of the wrench with the bolt head. Repeated drive and non-drive rotations tighten or loosen the bolt conveniently. The conventional unidirectional ratchet wrench may be turned over to reverse the drive direction.
Although the tapered coil spring 44 allows the slot 431 to be made shallower and smaller than using a normal coil spring, thereby allowing miniaturization of the conventional unidirectional ratchet wrench, the tapered coil spring 44 is significantly more expensive than a normal coil spring. The ratchet jaw 43 must be thick enough to accommodate the tapered coil spring 44 so limiting miniaturization of the conventional wrench and causing structural weakness to the ratchet jaw 44, thereby preventing application of the conventional unidirectional ratchet wrench to small sized bolts.
Further, the inner end of the slot 431 has to be precisely formed so production of the wrench conventional ratchet requires a precise casting process, linear cutting or LASER cutting, which significantly raises manufacturing cost and may even require two cutting processes during production.
Moreover, the retractable tab 45 of the conventional unidirectional ratchet wrench retracts into the slot 431 in a linear movement, so the abutting surface of the retractable tab 45 projects out from the recession 431 and provides only a small area for contacting the bolt head. Such structure may cause unexpected and unsafe slippage during use. Also, due to limited movement, the retractable tab 45 cannot be used on slightly rounded, damaged or non-standard sized bolt heads.
Each recess of the ratchet jaw 43 may be provided with two projections 432 to facilitate connection of a corresponding cover plate 46. When attaching the cover plates 46, the projections 432 are melted and welded with the cover plates 46. However, visible welding marks appear on and around the cover plate 46. Furthermore, the cover plates 46 do not reinforce the ratchet jaw 43 and may be removed by accidentally dropping the conventional ratchet.
With reference to FIGS. 11 and 12, U.S. Pat. No. 4,158,975, entitled to “Unidirectional Gripping Open End Wrench” discloses a D-shaped piece 50 movably mounted in a cavity defined in a head of the wrench and is connected to a helical compression spring 52. However, the wrench of the '975 Patent still needs a spring 52 to recover the D-shaped pieces 50, to assemble the wrench of the '975 is difficult. In addition, the D-shaped piece 50 of the '975 Patent is designed to abut completely with a flat of a bolt head with the straight edge. However, when the wrench of the '975 Patent is rotated in a slip action, the straight edge of the D-shaped piece 50 will push against one of the corners of the bolt head to cause the head of the wrench of the '975 Patent away from the bolt head. Consequently, the head of the wrench of the '975 Patent may disengage from the bolt head during the slip action and this will cause inconvenience to the operation of the wrench of the '975 Patent.
With reference to FIGS. 13 and 14, U.S. Pat. No. 5,018,412, entitled to “Open-End Ratchet Wrench” discloses a jaw portion 60 operatably mounted on an end of a handle element 62 and is connected to a spring 64. However, the wrench of the '412 Patent also needs a spring 64 to cause difficulty in assembling the wrench. In addition, multiple notches 602,612 separated from each other in 30 degree have to be formed in the jaws 60,61 for holding corners of the bolt head inside during a drive and non-drive direction, but the notches 602,612 will cause complicate in structure of the wrench of the '412.
With reference to FIG. 15, U.S. Pat. No. 4,706,528, entitled to “Adjustable Wrench” discloses a sliding jaw 70 slidably mounted on an end of a handle 72 and is connected to a coil spring 74 and a plate spring 76. The wrench of the '528 needs two springs 74,76 for the operation of the sliding jaw 70, so the structure of the wrench of the 528 Patent is complicated. In addition, when the wrench of the '528 Patent is applied to a tool having a hexagonal head, the head of the wrench of the '528 Patent will also be pushed away from the bolt head by the corners of the bolt head. Thus, the head of the wrench of the '528 Patent may disengage from the bolt head during the non-drive direction, so the '528 Patent has a ratchet function only when being applied to an object having a circular cross section. The '528 Patent will lose the ratchet function when being applied to a tool head having a hexagonal cross section and is inconvenient in operation.
With reference to FIG. 16, U.S. Pat. No. 385,595, entitled to “Pipe Wrench” discloses a jaw 80 slidably mounted on an end of a handle 82 and has multiple teeth. However, the pipe wrench of the '595 Patent can only be applied to rotate an object having a circular cross section, such as a pipe but cannot be applied to rotate a tool head having a hexagonal cross section.
To overcome the shortcomings, the present invention provides a unidirectional ratchet wrench to mitigate or obviate the aforementioned problems.